﻿rUTF.RSONIA 20 1 



gravid, the ovisacs swell very little, and they are only slightly 

 compressed in the basal part, which is largely enclosed between 

 the laminae of the gill. The ovisacs reach considerably beyond 

 the edge of the gill, and in this region they are curved back- 

 ward in a peculiar manner, subcylindrical, and tapering towards 

 a point directed backward at the hind end of the marsupium. 

 The marsupium has also a remarkably sharp edge. Placentae 

 not very solid. Glochidia lying all through the placental mass,, 

 of medium size, and subovate in shape." (Ortmann.) 



Type Lampsilis irideHa P. and F. 

 friersonia Ortmann, .\nn. Car. Mus., VIII, 1912, p. 318. 



Friersonia irideixa (Pilsbry and Frierson). 



"The shell is oblong, wider posteriorly, with the beaks 

 at the anterior two-ninths of the length, anterior end round- 

 ed ; posterior part sloping above, subtruncate at the end, 

 compressed below the hinge. Surface glossy, smoothish, 

 obliquely corrugated along the posterior slope, (but sometimes 

 very indistinctly so), and usually having a group of short, im- 

 pressed lines or furrows vertical to the basal margin, near the 

 middle of the disk. Of a dull straw or pale greenish color, 

 profusely marked wnth green rays, which are usually quite dis- 

 tinct and narrow. The valves are thin, nacre bluish-silvery, 

 very iridescent posteriorly. Cardinal teeth small, a single 

 rather stout one in the right valve, two more compressed and 

 generally subequal teeth in the left valve. Lateral teeth very 

 narrow, double in the left, single in the right valve. 



Length 49,- height 26, diam. 15 mm." (P. & F.) 



Type locality, Valles. Mexico. 

 L. iridella, Naut., XXI, 1907, pi. xii, two lower right-hand 



figs. 

 Lampsilis iridella Pilsbry and Frierson, Naut., XXII, 1908, 



p. 8t. 

 Friersonia iridella Ortmann, Ann. Car. Mus., VIII, 1912, p. 



319, fig. 19. 



This species "is related to U. popei and U. medelltniis. 



